Process and composition for producing a dyeable corrosion resistant surface on zinc and high zinc alloys



Patented July 26, 1949 PROCESS AND OOMPOSITIGNFDBi-PRODUG- ING A DYEABLE CORROSION RESISTANT" SURFACE ON I ZINC ALLOYS AND HIGH ZINC Earle R. McLean and David M. J enkinsflfr.) Pittse burgh, Pa., assignors to The Glark ThreadCom-T- pany, Wilmington, DeL, a corporation of-Delaware No Drawing. Application Jul-y,23,l947 Serial No. 763,168

r Claims.-

This invention relates to: dyed, corrosion rcsistant, metal surfaces of such metals as zinc and high zinc alloys, and more particularly it relates to a composition and process for filming or coating said metals and to the resulting product.

Zinc articles, when subjected to highly humid atmospheres or to actual contact with water, tend to develop a layer or crust of white zinc corrosion products which may be objectionable from the standpoint of appearance. More significantly, such corrosion products may interfere with the operation of articles which are designed to function with small tolerances. It is proposed, according to the invention, to produce a film on the surface of the articles by treating them with a solution or composition hereinafter described. The film acts as an inhibitor to protect the metal by preventing the formation of corrosion prodnets, and in addition, the film thus produced is amenable to further processing, in particular to dyeing.

It is a principal object of the invention to provide corrosion resistant articles of zinc and (high zinc alloys in a variety of attractive colors in which both the collor and the corrosion resisting film have good wash fastness andare resistant to Wear. Other objects and advantages will appear as the description proceeds.

In general, the invention comprises subjecting the metal to be treated to the action of an aqueous solution comprising a chromium trioxicle-containing compound, lactic acid and/ or soluble lactates, and a mineralacid. The solution has a pH of approximatelyLO, which is kept within narrow limits and which, together with the lactic acid concentration, constitute more or less critical factors for obtaining satisfactory films and colors. After such treating step the metal is washed, dyed while stillwet, dried, and subjected to a curing or heatingstep to fix the film and dye upon the surface of the metal.

Referring to the I solution or composition in detail, and to the chromium compound in particular, it is required that'the chromium trioxidecontaining compound be a water-soluble material,

ance to corrosion and which have good affinity for dyes. Commercially available chromium compounds maybe employed formaking up the composition; Where the expression chromium trioxide is recitedin the specification and the claims, it is intended to embrace both that particular compound andalso compounds inherently containing chromium trioxide, as may be determined by inspection of their chemical formula, an example of which; is sodium dichromate, NazCrzOw.

The lactic-acid concentration of thecomposition lies within narrow limits, the most suitable range belngfrom" about 0.24 to 2.17 g./l., with about1.9"g./l'. as the preferred concentration. Good dye afiinity has been obtained at a concentration of SJGgr/L, and higher concentrations up to about- 9 gr/l. maybe employed, although at the higher concentrations thecolor shade may be somewhatlight. Forisome purposes light shades, i. e., light in depth; may-be sultable. Beyond about 9 gz/l. the affinity for dyes rapidly decreases; Useful. results ,may be obtained with concentrations as'low: as 'O.12g,/l. The practice was'toemploy t n-85% solution oflactic acid in water as a stock solutionand to take a portion of this and dilute itas required. The stock solution had a pH of approximatelyZiQi and 1 cc. of it weighed ,13122 grams; 'Itwas found useful to dilute this solution in the ratio of 75 cc. of water to 2500: of solution'to. form a working solution (hereinafter referred'to as the 25% lactic acid solution), 13cc; ofwhichcontained about 0.24 g. of lactic'acid. Soluble lactates, such as sodium lactate, may beused'in placeof lactic acid. in

equivalentconcentrations, and itis to beunderpreferably chosen from the class consisting of tion, filmsare produced which show good resiststood thatreferences to lactic acid in the specification and claims are intended to embraceequivalent amounts of soluble lactates.

The preferred mineral acid .is sulfuric, although other acids such as nitric; hydrochloric, and phosphoric have useful application. A sufficient amount of acidiis employed to impart to the composition the required pH value. This amount is usually small anddepends upon the concentra tion-of lactic acid irrthecomposition. For example; in a composition containing 200 g. /l. of sodium dichromate =and- 1. 9l g./l. of lactic acid, the amount of sulfuric,acidrequired to produce a'pH of 1.0isaboutf5i63 g;/1.' In the case of sulfuric acid, the practice'Was-to emp1oya'92% stock solution; lcc. of w'hichweighed'lL68 a, and to dilute this solution asrequired. Preferably the solution was diluted lnaiiratio of cc. of "water to25'cc. of *the stocksolution to form a working means of alkaline plating processes.

solution (hereinafter referred to as the 25% sulfuric acid solution) containing about 0.42 g. of acid per cc. I V I As stated,the pH-of the composition must be closely controlled, this being necessary in order to produce a film having optimum dye affinity.

Excellent results are obtained at a pH of 1.0, and

a variation of 10.1 or $0.2 is possible. Below a pH of 0.65 and above pH 1.5 the results are not satisfactory.

The composition may be made up by forming a solution of the chromium compound in water, adding the lactic acid to this solutiornand then adding sulfuric acid to adjust the pH. Examples of various compositions and the results obtainable therewith are described below in Example 1.

Zinc and high zinc alloys are the preferred metals which may be treated according to the invention, and particularly good results are secured when these metals are in the form of castings. and stampings. Other zinc-containing materials may be processed, such as zinc-plated brass formed by Examples of high zinc alloys are (1) aluminum 4.01%, copper 1.00%, magnesium 0.03%, balance zinc; and (2) aluminum 4.01%, magnesium 0.04%, balance zinc. Alloys containing about 90 to 99.9% zinc are specially suitable to the treatment herein described. By the expression high zinc alloys, as employed throughout the specification and claims, is meant alloys containing a major portion of zinc. V

As stated, metal articles of the kind described may be made corrosion-resistant and dyed by subjecting the articles to the action of the above described compositions or solutions and then dyeing them in a bath containing the desired dye. As examples of articles suitable for processing according to the invention there may be mentioned slide fastener stringers, sliders, stops, and the like. It is important that the articles be clean before treating them, in order to avoid the presence of spots, blemishes, etc. in the final product. For this purpose'a cleaning step, in which alkaline cleaners are generally used, is employed in advance of the solution-treating step, after which the articles are rinsed with water and/or dilute acid. They are then subjected to the treating or filming step, usually by immersing them in a bath of the treating solution. The film that is thus formed on the metal surface is insoluble, or substantially insoluble, in water and tends to act as a corrosion inhibitor to protect the bare surface. Thereafter the articles are' rinsed with water and allowed to drain to reduce the drag-out loss attendant upon their removal from the treating bath. The articles should not be allowed to dry, as this would seriously affect the afiinity of the film for the dye. They are, therefore, dyed a few seconds after draining in a solution of an organic, water-soluble dye. The articles are then rinsed, allowed to dry, and subjected to a curing or heating step to fix the dyed film upon the article. I V g The foregoing process may be described in greater detail, step by step, as follows. In the cleaning step it is necessary to completely remove from the articles all grease, oil, dirt, oxide or other surface contaminants. Dilute alkaline cleaners such as caustic soda, sodium hexameta phosphate, tri-sodium phosphate, etc. have been found satisfactory for this purpose. As an example, a 1% by weight caustic soda solution at a temperature of about 200F. and a time of about 2 minutes gave excellent results. Temperatures and times of treatment, however, may vary. Sodium hexameta phosphate in an amount of about 0.5%, or sodium oleyl alcohol sulfate, or

both, may be added to the foregoing solution with good results. Preferably the articles are immersed in the cleaning solution and agitated durin the course of the operation.

Following the cleaning, the articles are rinsed with cold water to avoid carrying over the alkaline cleaning agent into the acid treating solution. A dilute .acid wash, for example, a 1 or 2% by weight solution of sulfuric acid for a few seconds at room temperatures, followed by a water rinse, is helpful to neutralize any alkali remaining on the articles. A small amount of free naphthalene sulfonic acid may be added to the sulfuric acid solution. Such acid wash also has a slight etching action on the metal surface and serves to keep the pH." of the treating solution under better control. p

The treating step is generally carried out for a time sufficient to produce the desired film or coating on the surface of the metal articles. The treating time is variable, but in practice may be about 15-20 seconds at room temperatures, with seconds as the preferred period. Room temperatures, say 75 F. :5 F., are preferred. Lower temperatures are permissible, although in this case the treating time may have to be increased proportionately. Mild agitationof the articles in the treating bath is desirable to obtain a uniform coverage.

After the treating step the articles should be drained to permit recovery of as much solution as possible without allowing them to dry. 'In practice, draining times up to seconds may be permissible. Thereafter the articles may be rinsed with water to fully remove the treating solution, and in this operation care must be taken to avoid disrupting the film, which at this stage is rather soft. Preferably the rinsing is accomplished by immersing the articles in a bath of water at room temperatures, although lower and higher temperatures may be used. The rinsing period is usually on the order of about 10 seconds.

Following the rinsing, the articles, while still wet, are immersed in a dye bath for a time sufficient to dye the film, usually about 3 to 6 minutes, and preferably at room temperatures. The bath may be prepared by thoroughly dissolving the usual amount of dye, for example about 0.2% by. weight, in a small amount of hot water and then adding this solution to the water in the dye bath. The pH of the dye bath is generally maintained at 4.0:05, and may be adjusted with suitable materials, say acetic acid or aqua ammonia according to the pH of the initial dye solution, which may vary from 2.0 to 11.0 depending upon the particular dyestufi. Agitation of the bath is helpful. A variety of colors are possible, such as black, violet, blue, green, red, walnut brown, chestnut brown, cinnamon brown, grey. and some of the dyes corresponding to these colors are as follows, the Color Index number, where known, being given in parenthesis: Palatine Fast Black WANA Cone, Supramine Fast Black BRA, Wool Violet 4 EN (698), Alizarine Sapphire (1054), W001 Blue C. G., Alizarine Fast Red S. Pdr. 110% (1034), A20 Fuchsine 63 New (5'7), Wool Red 40F (184.), Azo Rubine (1'79), Milling Red-R (430), Acid Anthracene Brown WSGA+Palatine Fast Black WANA, Chrome Fast Brown 3 B, Acid Anthracene Brown WSGA, Fast Acid Brown RG,

Alphazurine A (714), Alkali Fast Green 2 G aims-1o (735), Alizaririe cyanone Greene as. (1078), Naphthol Green B (5), etc. Where articlessuch as slide fastener stringers attached to cotton stringer tapes are dyed, it -is preferable that the dyes should have no aflinity for cotton in order to avoid staining the tapes. In such case, dyes commonly used for dyeingsillr, woo1, or other protein fibers, such as acid, chrome, mordant, mordant-acid, and chromiferous'dyes, may be employed. Rinsing off the excess dye from the articles is readily accomplished-by employingo'ne or tworinses withwate'r at room temperature. If a dull finish is desired, the rinsingmay'be car ried out at higher temperatures,;say':1409 F., for.

about seconds. After rinsing,.the'-articles may be dried at temperaturesupito 140-150 As a final step, the articles are cured by heatinglthewsarne, a preferred. treatment being at a temperature of about-.200"F. .forabout minutes. Higher or'low'ercuring.temperatures are permissible, say 150 to 250 F.,.provided.the time is suitably adjusted. Higher. temperatures will generally require lower times, and vice versa. The main consideration is to fix the .film, and the. dye upon the-metal surface to secure the optimum corrosion resistance and color effect.

It is desirable in. many cases, particularly with pure zinc articles, .to subject themin advance of the cleaning step to a pre-treatment with an acidsuch as dilute nitric acid to improve the shade of the dye, espeoiallyinthe case of the lighter shades and also .to render, the surfaces of the articles more suitable for filming, as by eliminating spots.

In the case of oily articles'or those containing residual soap, or Which in the manufacturing stage, have been under burnished or over burnished or have beensubjected to various casting difliculties, it is desirable to subject them initially to a .precleaning with dilute neutral or slightly alkaline cleaners at boiling or nearboiling temperatures. They may then beri nsed, pretreated with dilute nitric acid, rinsed again, cleaned, subjected to the dilute acid wash (sulfuric acid). above described, then to the solution treating or filming step, etcsuch precleafiing serves to remove the oil and soapy material adhering to the surfaces of the articles, while the nitric acid tends to etch the cleaned surfaces, to remove oxide films, etc.

The invention may be illustrated by'the followingexamplesz' Example 1 This example illustrates anuniber or treating solutions containing varying amounts of lactic acid, as listed below. In each case the solution contained 500 cc. of. water and .100 gr. of. sodium dichromate. The pH of each solution, prior to adjustment, is listed, and the amount of. sulfuric. acid required to adjust each solution .to a: pH.

of ;1.0 is also listed.

Another solution; labeled 511, was prepared containing 8.2-cc. or. amixture crud es. 435% Example 2 To illustrate the effect of the pi-I of the treathis solution, eight solutions werepr'epared, eac'h comprising 500 cc. of Water, g. of sodium dichromate, and 1 cc. of lactic acid (solution 1A of Example 1). Each solution was adjustedv with sulfuric acid to the pH value listed below and then employed to treat slide fastener stringers. Thereafter the stringers were dyed, using black and walnutshades, and the dye affinity observed. The results are as follows:

pH of Soln. f Dye Shade Results.

- Fair. Walnut Fair to good.

Eit'a'mple 3 This example shows the variation that is pos sible in the choice of mineral acid for the treating solution. Zinc alloy slide fastener parts were cleaned with alkali, rinsed with acid, and then subjected to treatment with solution 4A described in Example 1, except that the pH of the solution was adjusted to pH of 1.0 with hydrochloric acid instead of sulfuric acid. Thereafter the parts were dyed navy blue, good results being obtained. The foregoing Work was repeated with nitric acid and then with phosphoric acid substituted for the hydrochloric acid, and in each case the results were good.

Example 4 a The corrosion resistance of Zinc alloy articles treated according to the invention is illustrated by the following example. Zinc alloy slide fastener stringers and parts were processed with solu tion 4A (pH 1.0) described in Example 1, one sample of each article being left unprocessed for control purposes. Thereafter the samples, except the controls, were dyed a number of shades including black, navy blue, walnut and chestnut. The treatment of the stringers may be set forth as follows:

Clean: 1% sodium hydroxidemlii sec. at lilo-200 F., rinse.

Acid: 1% sulfuric acid, 15 sec. at 75 F., rinse-.1

Treat: Solution 4A, 20 sec. at 75 F., rinse.

Dye: Color as specified, 5 min. at 75 F., pI-idl,

rinse and dry.

Cure: 15 min. at 200 F.

The treatment of the parts isas follows:

Pretreat: 1 nitric acid, 15 sec. at 75 F., rinse. Clean: 1% sodium hydroxide 0.5% sodium oleyl alcohol sulfate 0.5% sodium hexameta:

phosphate, 2 min. at 190-200 F., rinse. Y

Solution 5A contained 2.17 grams per Acid: 2% sulfuric acid, sec. at 75 F., rinse.

Treat: Solution 4A, sec. at 75 F., rinse.

Dye: Color as specified, 5 min. at 75 F., pHJLl,

rinse and dry.

Cur e: 15 min. at 2q0 F.

Three stringers and'three parts were processed with each color. each color were then saved as processed control samples while all the other samples, including the unprocessed controls, were subjected to corrosion tests? The latter comprised the following procedure: ll

The test specimens were sealed in'a container which had been adjusted by the use of a saturated potassium sulphate solution to produce a relative humidity of 95% at 120 F. The samples were exposed under these conditions for 22 hours a day and then allowed to cool, while still sealed, to room temperature for 2 hours a day, causing water vapor to condense on the parts. This test was conducted for twenty-eight days with weekly examinations. The degree of corrosion, after each examination, was visually evaluated and recorded.

Example 5 In this example is shown the wash fastness of articles treated according to the invention. A number of zinc alloy slide fastener stringers were treated and dyed as described in Example 4. They were then subjected to two series of wash fastness tests. The first series comprised a group of four tests at 160 F'., using 0.5% by weight of oleate soap and 0.25% by weight of sodium hexametaphosphate for minutes. After each test, samples were taken out of the bath, rinsed and dried. Some of the test samples were removed and the remainder run again. The second series of tests was like the first series except that the temperature was 212 F.

The results showed excellent wash fastness of all the samples. In fact, the washed articles appeared to be brighter and to have a deeper shade of color than the unwashed articles.

Example 6 Preclean: 0.5% sodium salt of lauryi alcohol sulfate +0.25% sodium hexameta phosphate for 45 sec. at 200-210 F. Rinse.

Pi'etreat: 3% nitric acid for 15 sec. at 75 F.

Rinse.

Clean: 1% sodium hydroxide +05% sodium oleyl alcohol sulfate +05% sodium hexametaphosphate, 2 minutes at 190-200 F.

Acid: 2% sulfuric acid +05% free naphthalene sulfonic acid, 15 sec. at 75 F.

Treat: Solution 5A, 20 sec. at 75 F.

Dye: Shades as required.

Good coverage of secured,

One stringer andone part of both the film and the dye were either continuous'or batch operation, particular-j ly the former. I

It will be understood that, unless otherwise indicated, variations in the ingredients and conditions of the process are permissible within the scope of the invention. 1

In the light ofthe foregoing'description, following is claimed:

1. A composition for producing a corrosion resistant coating having good dye affinity on the surface of zincrand high zinc alloys which comprises essentially a water soluble chromium trioxide-containing compound selected from the class 'COHSiStiHgTOf chromic acid and salts thereof, saidcompound being present in an amount equivalent to about grams per liter of chromium trioxide; about 1 to about 9 grams per' liter of lactic acid, an amount of strong mineral acid sufficient to impart a pH of 0.65 to 1.5 to the com position, and the balance water.

2. A composition for producing on zinc and high zinc alloys a corrosion resistant surface having good affinity for dyes which comprises essentially about l50'grams per liter of chromium trioxide, about 1 to about 9 grams per liter of lactic acid, an amount of sulfuric acid sufficient to impart a pH of about 0.65 to 1.5 to the composition, and the balance water.

3. A composition for producing a corrosion resistant surface having good affinity for dyes on zinc and high zinc alloy castings and stampings which comprises essentially a water soluble dichromate containing about 150 grams perliter of chromium trioxide, about 1 to about Qg rams the per liter of lactic acid, an amount of sulfuric acid sufficient to impart a pH of about 0.65 to 1.5 to

the composition, and the balance water.

4. A composition for producing acorrosion resistant surface having good affinity for dyes on zinc and high zinc alloy castings and stampings, which comprises essentially about 200 grams per liter of sodium dichromate, about 1.9 grams per.

liter of lactic acid, an amount of sulfuric acid sufiicient to impart a pH of about 1.0 to the composition, and .the balance water. 7

5. A process for rendering the surface of zinc and high zinc alloys corrosion resistant. and amenable to dyeing which comprises subjecting the metal to the action of the composition described in claim 1 for a time suflicient to produce a film on the surface of the metal, and then washing said surface.

6. A process for producing corrosion resistant surfaces on zinc and high zinc alloys and coincidently rendering such surfaces amenable to dyeing which comprises subjecting the metal to the action .of the composition described in claim 3 for a time sufhcient to produce a film on the surface of the metal, and then washing said'surface.

7. A process for producing corrosion resistant surfaces on zinc and high zinc alloy castings and- 10 of the metal and then dyeing the treated metal ings and stampi Wh Still W n th n c rbefore said filmed surface is dry. ing the castings and stampings.

9. A process for producing a dyed, corrosion EARLE R. McLEAN. resistant article of zinc and high zinc alloys which DAVID M. JENKINS, JR. comprises subjecting the article to the action of 5 the composition described in claim 2 for a time REFERENCES CITED Sumcient to produce film on the surface of the The following referemees are of record in the article and then dyeing the treated article before file of this patent: said filmed surface is dry.

10. A process for producing dyed, corrosion re- 10 UNITED STATES PATENTS sistant castings and stampings of zinc and high Number Name Date zinc alloys which comprises subjecting the cast- 2,021,592 Dubpernell et a1. Nov. 19, 1935 ings and stampings to the action of the compo- 2 0 3 Meyer et aL July 27, 1937 sition described in claim 4 for a time sufficien 2,236,549 Darsey et al. Apr. 1, 1941 to produce a film on the surface of the castings 15 2 3 3 King Jan 29, 1946 and stampings, rinsing said composition from the 2 393, 4 Thomas et Jan 29, 1946 castings and stampings, dyeing the treated cast- 2,433,723 Wieczorek Dec. 30, 1947 

